The present invention relates to mechanical fastening systems, and more particularly to automotive seat belts. Yet more particularly, the present invention relates to a detector of a fastened state of a seat belt fastening system.
Automotive seat belts generally include first and second seat belt components which are selectively fastened together by a fastening system in order to retain a passenger seated in the event of an untoward incident involving the motor vehicle. Typically, a seat belt has the following attributes. A first seat belt component includes a first section of seat belt and a shoulder harness belt which are, respectively, connected at one end to immovable anchorages and at the other end to a tongue. The tongue is composed of a strong, rigid metallic material, and has a latch aperture formed therein. A second seat belt component includes a second section of belt which is connected at one end to an immovable anchorage and at the other to a buckle. The buckle has located therewithin a spring loaded latch and externally a manual release for the latch. In operation, the tongue is placed into the buckle until seated, whereat the latch has entered into the latch aperture so as to firmly and positively locate the tongue irremovably with respect to the buckle, unless manually released via the release. The buckle and the tongue collectively form a seat belt fastening system which is critical to operation of the seat belt.
Examples of seat belt fastening systems include U.S. Pat. Nos. 4,094,046; 4,575,908; and 4,899,424.
A concern is whether or not a seat belt has been properly fastened at the fastening system. That is, whether or not the tongue is properly seated in the buckle such that the latch of the buckle is positively located in the latch aperture of the tongue, wherein the latch engagement prevents the tongue from backing out of the buckle unless intentionally released by the seated occupant of the vehicle. U.S. Pat. No. 4,196,500 describes a seat belt buckle having a leaf switch which is biased normally open, but is bent against the biasing by the forward end of the tongue, such that contact is made when the tongue has been seated sufficiently far into the buckle that the latch must be located in the latch aperture.
Latch engagement detection may, for example, take the form of an appropriate circuit causing a warning light and/or sound to inform the seated occupant of the vehicle that the seat belt is not properly fastened. Mechanical switches, in general, are susceptible to wear in terms of the moving component and in terms of the electrical contacts. Therefore, what is needed in the seat belt art is a latch engagement detector which is contactless.
The present invention is a contactless latch engagement detector for a seat belt operating on the principle of magnetosensitivity.
It is known that magnetosensitive devices, such as Hall effect devices and magnetoresistors have an electrical response related to proximity and direction of a magnetic field, respectively. For example, magnetosensitive devices, such as magnetoresistors (MRs) and Hall effect devices have been used as non-contacting position and angle sensors with respect to a rotating toothed wheel, as for example exemplified by U.S. Pat. No. 5,404,102. In such applications, the magnetoresistor (MR) is biased with a magnetic field and electrically excited, typically, with a constant current source or a constant voltage source. A magnetic (i.e., ferromagnetic) object moving relative, and in close proximity, to the MR, such as a toothed wheel, produces a varying magnetic flux density through the MR, which, in turn, varies the resistance of the MR. The MR will have a higher magnetic flux density passing through it, and, consequently, a higher resistance when a tooth of the moving target wheel is adjacent to the MR than when a slot of the moving target wheel is adjacent to the MR.
The magnetosensitive latch engagement detector according to the present invention includes, within the seat belt buckle, a magnetosensitive switch composed of a magnetosensitive device and at least one biasing magnet adjacent the magnetosensitive device. In addition, the latch engagement detector also includes, within or external to the buckle, an electronic circuit for driving the magnetosensitive device, and a flux bar composed of a ferromagnetic material having a high magnetic permeability which is associated with a movable component of the seat belt.
In operation, the electronic circuit drives the magnetosensitive device, wherein a first level of output is registered from the magnetosensitive device responsive to an absence thereat of the flux bar. The flux bar is associated with a moving component of the seat belt, as for example being in the form of the buckle latch or the tongue. When the tongue is seated fully into the buckle, the flux bar will have moved into close proximity to the magnetosensitive device, thereby causing the magnetic field of the biasing magnet(s) to be reduced at the magnetosensitive device. Since the signal output of the magnetosensitive device is responsive to the magnetic flux passing therethrough, the electronic circuit registers a second output signal from the magnetosensitive device indicative that the tongue is properly seated in the buckle and that the latch must be properly engaged.
Accordingly, it is an object of the present invention to provide contactless latch detection for the tongue and buckle which is indicative of whether the fastening system of the seat belt is fastened.
This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment.